This invention relates generally to refrigeration systems and equipment for use in rail cars, trucks and other transport vehicles to maintain perishable items such as food products at a selected refrigerated temperature. More particularly, this invention relates to an improved refrigeration system having modular components which can be installed quickly and easily into a rail car or the like to support cryogenic refrigerant and to control flow of sublimated cryogenic gas.
A wide variety of perishable items particularly such as food products are routinely shipped in a chilled or frozen state to avoid product spoilage and/or contamination. In this regard, refrigeration systems for use in transport or shipping vehicles such as rail cars, trucks, and the like are well known and have been widely used for many years. In one common form, such refrigeration systems have utilized conventional mechanical refrigeration units for maintaining a controlled temperature within an insulated storage container or compartment. However, mechanical refrigeration units are relatively costly and require significant maintenance over a typical service life. Moreover, mechanical refrigeration equipment normally exhibits relatively high power or energy consumption, wherein an appropriate fuel or electrical power source for the refrigeration unit must be carried with the shipping vehicle.
In recent years, non-mechanical refrigeration systems have acquired significant commercial interest in efforts to avoid the cost and related complexities associated with standard mechanical refrigeration equipment. In a non-mechanical system, the rail car or the like is modified to carry an expendable supply of a cryogenic material, particularly such as carbon dioxide in solid form, commonly known as dry ice. The cryogenic material is supported in close association with the items being shipped to maintain a sufficiently low temperature to prevent spoilage. Over a period of time which may include several days, the solid carbon dioxide sublimates into the form of cryogenic gas which is normally circulated over or about the perishable items prior to exhausting to the atmosphere through suitable vents. Such non-mechanical refrigeration systems as typified by the prior art are described, by way of example, in U.S. Pat. Nos. 3,561,226; 4,761,969; and 4,704,876.
While non-mechanical refrigeration systems using cryogenic materials offer significant advantages in use, as described above, the structural components used to support the cryogenic material and/or to control the flow of sublimated cryogenic gas have been relatively complex and costly to install within a rail car or other shipping vehicle. Moreover, some prior system arrangements have envisioned multidirectional gas flow paths which are difficult to implement in a manner assuring substantially uniform low temperature throughout the storage space, especially when the storage space is fully loaded with the perishable products.
There exists, therefore, a significant need for further improvements in non-mechanical refrigeration systems of the type used to refrigerate perishable products in a shipping container such as a rail car or the like, particularly with respect to relatively simple and easily installed structures for supporting cryogenic material and for distributing resultant cryogenic gases relatively uniformly throughout a storage compartment. The present invention fulfills these needs and provides further related advantages.